This invention relates to a control system for a vehicle safety device or the like.
As disclosed in Japanese Laid-Open (Kokai) Patent Application No. 193743/1990, a control system for an air bag (vehicle safety device) comprises an acceleration sensor, an amplifier for amplifying an output of the acceleration sensor, an analog-to-digital converter (ADC) for converting the amplified acceleration signal to a digital signal, and a microcomputer for receiving the acceleration signal from the ADC and effecting an acceleration evaluation. The microcomputer receives the acceleration signal at a predetermined cycle, and integrates it, and compares this integral value with a threshold value. This integral value represents a change in vehicle speed, and increases in the decelerating direction when a collision has occurred. When the integral value increases in the decelerating direction and exceeds the threshold value, the microcomputer judges that a collision has occurred, and outputs a trigger signal, thereby expanding the air bag.
In general, an output of each acceleration sensor of the type used in the above control system was irregular, and was required to be corrected individually. Although not disclosed in the above Patent application, heretofore, the output of the acceleration sensor was compared with that of a reference sensor, and a gain of the amplifier was adjusted based on a result of the comparison, so that the acceleration signal of the former inputted into the microcomputer would be identical with that of the latter, so that the acceleration evaluation can be effected with high accuracy.
Recently, a system using an EEPROM has been developed in order to effect the gain adjustment comparatively simply and accurately. Specifically, in this system, a gain corresponding to an output characteristic of the acceleration sensor is written into a predetermined memory area of the EEPROM. The acceleration from the acceleration sensor is multiplied by the gain so as to be corrected, and the acceleration evaluation is effected based on this corrected acceleration. Although the above EEPROM is capable of storing data stably, the data stored in the EEPROM are threatened with a possible breakage after the passage of a long period of time, and therefore a counter-measure for the possible breakage is demanded.
As the prior art relating to the present invention, Japanese Laid-Open (Kokai) Patent Application No. 259902/1990 discloses a data storing device for a vehicle control system, and it also discloses, as one specific example, a device for storing a gain of vehicle speed in a constant-run control system. In this storing device, the gain of the vehicle speed can be rewritten while the vehicle is in a running condition. This storing device includes first to fourth memories, each of 8 bits. Identical data, as the gain, are stored in the first and third memories, and their complementary numerical values (inverse numerical values) are stored in the second and fourth memories. The microcomputer receives the vehicle speed and multiplies the vehicle speed by this gain to obtain a corrected vehicle speed. The gain is determined as follows. First, the data in the first memory and the data in the second memory are read, and then it is judged whether or not these data are in complementary relation. If the judgment result is "YES", the data in the first memory is used as the gain. In contrast, if the judgment result is "NO", it is then judged whether or not the data in the third and fourth memories are in complementary relation. If the judgment result is "YES", the data in the third memory is used as the gain. In contrast, if the judgment result is "NO", the data in all memories are initialized.
In the system of the above Laid-Open Patent Application No. 259902/1990, the gain is adjusted in accordance with a running condition of the vehicle (vehicle speed), and therefore the system is different in a premised technique from the present invention which relates to the storage of the gain for acceleration. In the present invention, the identical data are stored in the EEPROM for a long period of time as a premised technique. In the above Laid-Open Patent Application No. 259902/1990, only when at least one pair of data are in complementary relation, one of the pair of data is used as the gain and therefore reliability is low.
Japanese Laid-Open Patent Application No. 269641/1989 discloses, as another related prior art to the present invention, a device for storing a failure judgment data of an air bag controlling system. This storing device comprises a non-volatile memory (NVRAM), into which the failure judgment data of the air bag device is written. This storing device has three or more of memory areas A, B, and C. Each of the memory areas A, B, and C is of 8 bits. The failure judgment data is written into the memory area A, and an identical failure judgment data (but shifted or rotated by one bit with respect to the data in the memory area A) is written into the memory area B. Another identical failure judgment data (but further shifted or rotated by another one bit with respect to the data in the memory area B) is written into the memory area C. Then, the failure judgment data in all these memory areas are read, and then it is judged whether or not all of these data are identical with each other. If the judgment result is "NO", an alarm device is actuated in order to indicate that the storing device is subjected to a failure. At the same time, failure data are determined by the rule of majority.
The above Laid-Open Patent Application No. 269641/1989 relates to the device for storing a failure judgment data of an air bag controlling system, and therefore is different in a premised technique from the present invention. According to the present invention, it is a premised technique which relates to the storage of gain for acceleration from the sensor and this gain is stored in the EEPROM. In the Laid-Open Patent Application No. 269641/1989, data is determined merely by a majority, and therefore reliability of the data is low.